Flying a toy helicopter inside an accelerating train Scenario:
You ride in a train, you have this helicopter toy. The train is not yet running when you flew your helicopter on a constant altitude (say 1 meter above the train's floor).
Question:
What will happen on the flying helicopter toy when the train accelerates?


*

*Will it stay relative to you and the train?

*Will it move backward relative to you and the train and bump to the rear part of the train?

*Will it move backward relative to you and the train for few seconds and then stay?

*Any other thoughts?
 A: The question Manishearth mentions is certainly closely related.
If the helicopter is flying then it is affected only by the air around it. Experience of riding in trains suggests that when the train starts the air moves with the train - at least I don't recall feeling any air movement when the train starts.
So the answer is either 2 or 3 depending on how fast the helicopter is affected by the air around it. When the train starts the helicopter is initially unaffected so the train passengers see it start to move towards the rear of the train. As the train accelerates the helicopter will feel an increasingly strong wind blowing from the rear to the front of the train, and this wind will start to accelerate the helicopter towards the front of the train. Whether the helicopter accelerates fast enough to avoid being hit by the rear of the compartment depends on how fast the wind accelerates it.
A: In modern trains, with closed windows and doors, between carriages, the air in the carriage moves en block, much as it would in a plane, before or after pressurization, or a car, with windows closed, and no blowers on, or vents open.
The air does not rush to one end of the carriage, leaving a partial vacuum at the other end. 
Since the helicopter is very light, and set to hover, at a fixed point in the air, its momentum change will be very small. I suspect there will be very little movement.
You could try this using a Helium balloon.
This could even be in a car, if the car has no air leaks.
I am not sure if they would let you on a plane, with a Helium balloon, so will not suggest that!!!!!
There might be a small difference, since the helicopter is using energy to hold it in the air, at a set position, relative to the air.
Just my conclusion on a logical basis, have made no tests.
A: 2:it will move backward relative to you and the train and bump to the rear part of the train
